One of the primary steps in the fabrication of modern semiconductor devices is the formation of a thin layer on a semiconductor substrate by chemical reaction of gases. Such a deposition process is referred to generally as chemical-vapor deposition (xe2x80x9cCVDxe2x80x9d). Conventional thermal CVD processes supply reactive gases to the substrate surface where heat-induced chemical reactions take place to produce a desired layer. Plasma-enhanced CVD (xe2x80x9cPECVDxe2x80x9d) techniques, on the other hand, promote excitation and/or dissociation of the reactant gases by the application of radio-frequency (xe2x80x9cRFxe2x80x9d) energy to a reaction zone near the substrate surface, thereby creating a plasma. The high reactivity of the species in the plasma reduces the energy required for a chemical reaction to take place, and thus lowers the temperature required for such CVD processes as compared to conventional thermal CVD processes. These advantages are further exploited by high-density-plasma (xe2x80x9cHDPxe2x80x9d) CVD techniques, in which a dense plasma is formed at low vacuum pressures so that the plasma species are even more reactive. xe2x80x9cHigh-densityxe2x80x9d is understood in this context to mean having an ion density that is equal to or exceeds 1011 ions/cm3.
Because these processes are used in the precise manufacture of small-scale devices, it is especially desirable to limit the incidence of damage to the substrates during processing. A common source of damage can be attributed to the presence of particles on the substrates. With the development of integrated circuits having feature sizes as small as 0.18 xcexcm and the industry continuing to develop circuits with even smaller features, even particles smaller than about 0.1 xcexcm can have a significant detrimental effect on overall device yield. Some estimates suggest that particle contamination may be responsible for more than 80% of all product yield loss.
To reduce the level of particle contamination and thereby increase device yield, methods have been developed to remove particulate contaminants as part of wafer preparation. For example, a common technique for removing such contamination uses wet chemical cleans. More recently, mechanical techniques have been developed, such as the CryoKinetic aerosol method, which has been incorporated into some integrated-circuit manufacturing lines to enhance yield and reduce defects. With this method, an array of cryogenic aerosol jets having frozen clusters of a mixture of argon and nitrogen is directed at the wafer. The contaminant particles are dislodged from the wafer when impacted by the clusters.
Such methods fail, however, to address the underlying problem of how the wafers become contaminated in the first place. This may be due to aspects of the wafer processing that vary according to different specific procedures. In order to identify the root causes of particle contamination, one procedure has been to examine the contaminated wafers to identify the composition of the particles and thereby identify the processing step at which they were incorporated into the layers. Such procedures have taken precise cross sections through the particles and then used techniques such as scanning electron microscopy, energy dispersive spectroscopy, or focused ion-beam spectroscopy to identify the source of the contaminant.
These techniques are time-consuming and generally inefficient. There remains a need for a method that provides real-time monitoring of particle performance during the manufacturing processes, which can be used to identify the root causes of particle issues efficiently and thereby develop particle-robust process recipes.
Embodiments of the invention therefore provide methods for identifying the root causes of particle issues and for developing particle-robust process recipes. This is achieved with methods that permit identification of a source of particle contamination in a particular recipe used for processing a substrate with a substrate processing system. In one set of embodiments, the presence of in situ particles within the substrate processing system is detected over a period of time that spans multiple distinct processing steps in the recipe. The time dependence of in situ particle levels is determined from these results. Then, the processing steps are correlated with the time dependence to identify relative particle levels with the processing steps. This information thus provides a direct indication of which steps result in the production of particle contaminants so that those steps may be targeted for modification in the development of particle recipes. In another set of embodiments, multiple recipes are compared by using this technique to identify particle sources. More desirable recipes are thereby discriminated from less desirable recipes according to the relative particle levels that result from corresponding processing steps.
In different embodiments, the in situ particles are detected against a bright field or a dark field. These different embodiments may use different particle sensing techniques. In one embodiment, particles are detected against a bright field during one processing step and detected against a dark field during another processing step. The method may be used with high-density-plasma chemical-vapor-deposition substrate processing systems, in addition to other systems.
These techniques have been used in the development of improved process recipes. One example of such improvements is related to the frequency of a clean cycle when a process chamber is used to process multiple substrates. Particle contamination is significantly mitigated by using a cycle in which a single cleaning procedure is performed between deposition procedures on more than two substrates, provided the cleaning procedure is performed for a period of time greater than or equal to 150 seconds. Another example of an improvement is related to how the process chamber is purged for a cycle in which a silicate glass layer is deposited on a plurality of substrates. The cyclic process includes seasoning the process chamber, depositing the silicate glass layer by plasma deposition, purging the process chamber, and cleaning the process chamber. The purging is performed without a flow of SiH4. In one embodiment, the plasma deposition uses substantially only side sources to provide the deposition gases to the chamber.
Methods of the invention may be embodied in a computer-readable storage medium having a computer-readable program embodied therein for directing operation of substrate processing system. Such a system may include a process chamber, a plasma generation system, a substrate holder, a gas delivery system, and a system controller. The computer-readable program includes instructions for operating the substrate processing system in accordance with the embodiments described above.
A further understanding of the nature and advantages of the present invention may be realized by reference to the remaining portions of the specification and the drawings.